1. Technical Field
The present invention relates to ceramic composites having superior mechanical characteristics in a room-temperature to medium/high-temperature range, employed as high wear resistance/low-friction ceramic materials in applications including diverse structural components, machining tools, sliding components, and mold-die materials; the invention also relates to methods of manufacturing such composites.
2. Description of the Related Art
Materials in which particles of a solid lubricant such as carbon have been dispersed into a ceramic matrix such as silicon nitride to improve the frictional coefficient and relative wear rate of the materials have been known to date.
For example, materials having outstanding frictional characteristics and wear-resistant properties, derived from composites of silicon nitride and titanium nitride together with 0.5 to 20 wt. % graphite and carbon, are reported in Japanese Unexamined Pat. App. Pub. No. 2003-34580. Nevertheless, sinter test samples of powders prepared under the conditions set forth in Pat. App. Pub. No. 2003-34580 were characterized using a scanning electron microscope at a magnification of 2000, whereupon numerous pores of 20 μm or greater diameter were observed, with the open porosity being a large 3% or more, which evidenced that it would be impossible to use the material for molds.
Meanwhile, a super-tough material in which 0.5 to 6 wt. % C, Cr, Mo, W, Al, Ti and Ni are incorporated as an oxidation-resistant alloy into alumina and zirconia is reported in Japanese Unexamined Pat. App. Pub. No. S60-100646; nevertheless, with the carbon content being a slight 0.1 to 0.2%, the material lacks the lubricity for molds.
In addition, a material that excels in resistance to wear, in which 2 to 50 wt. % carbon of 5 μm or greater grain size has been added to silicon carbide, is reported in Japanese Unexamined Pat. App. Pub. No. H09-87029, while a material in which 3 to 30 wt. % graphite of 3 to 6 μm average crystal-grain size has been dispersed within a titanium carbide matrix is reported in Japanese Unexamined Pat. App. Pub. No. H05-301773. Nevertheless, with the average crystal-grain size of the carbon being a large 3 μm or greater, in processing the material into a desired form the surface roughness is affected by the grain size, which is prohibitive of producing on the material reflective surfaces of 10 nm or less roughness average.
Presented in Japanese Unexamined Pat. App. Pub. No. H10-231174, furthermore, is a material in which graphite and boron nitride are dispersed into a non-oxide ceramic, between boundary layers of which an iron compound (such as an iron oxide or silicide) is interposed. Owing to the inclusion of iron, however, this material suffers from problems such as deterioration due to oxidation, and compromised stability at high temperatures, making it unfit for use as a mold-die substance.